CMOS light sensor and operation method thereof

ABSTRACT

A CMOS light sensor and the operation method thereof are disclosed. The CMOS light sensor has a plurality of light sensing lines and a plurality of capacitor lines. Each light sensing line has a plurality of light sensors such that the number of capacitors in each capacitor line is smaller than the number of light sensing cells in each light sensing line. The capacitors are used for holding a portion of the potentials produced by the light sensing cells due to illumination. The method of operating the CMOS light sensor includes transferring the data captured by the light sensing line to the capacitor line and reading out the data according to a pre-defined order so that the leakage of charges from the capacitor is reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Taiwan application serial no.91116948, filed on Jul. 30, 2002.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a CMOS light sensor and the operation method thereof. More particularly, the present invention relates to a CMOS light sensor and operation method that uses segment processing.

2. Description of Related Art

Most light sensors are classified into two major types, a charge-coupled device (CCD) or a CMOS light sensor. In a conventional CCD sensor, each light sensing line are assigned a group of shift registers for holding the charges produced by the CCD sensing line. In general, the amount of charges produced by the CCD sensor depends on the strength of illumination. Once the charges are fully transferred to the shift registers, the charges are sequentially shifted away from the shift registers to the circuit in the next processing stage. Similarly, as shown in FIG. 1, each CMOS light sensor 10 has a plurality of light sensing lines (12 a, 14 a and 16 a) and each has a functional element similar to the shift register in the charge couple device. However, instead of shift registers, these functional elements are capacitors.

The structure of the CMOS light sensor 10 and the conventional CCD sensor are almost identical except the deployment of a capacitor in the former instead of a shift register. Hence, the method of operating the CMOS light sensor 10 is very similar to the method of operating the CCD sensor. The CMOS sensor 10 is exposed to light so that the sensing cells (such as 120 a, 122 a, 140 a, 142 a, 160 a and 162 a) in the light sensing lines (12 a, 14 a and 16 a) generate an amount of electric charges in proportional to the intensity of illumination. Thereafter, various sensor cells (such as 120 a, 122 a, 136 a and 138 a) within the same light sensing line (such as 12 a) are sampled individually to reproduce a corresponding electric potential. The capacitors within the aforementioned capacitor line (such as 12 b) are actually storage device for registering the sampled electric potential.

In general, the capacitor line registers the resultant electric potentials produced by the entire light sensing line all at once but the electric potentials within the capacitor line are read out sequentially. Therefore, time to read out all of the potentials within the capacitor line increases with the number of sensor cells in a light sensing line. Since charge leakage occurs on most capacitors, the total number of charges drained away from the capacitor increases with time. If too many charges leak away from the capacitor, the actual stored data (electric potential) may be seriously distorted.

SUMMARY OF INVENTION

Accordingly, one object of the present invention is to provide a CMOS light sensor and operation method thereof. The CMOS light sensor has a capacitor line with a count of capacitors smaller than the count of light sensing cells in a light sensing line. Hence, all the data produced by the light sensing line can be read out in a few reading operations. Ultimately, data retaining period of data within each capacitor is shortened considerably when compared with a conventional technique.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a CMOS light sensor. The CMOS light sensor has a light sensing line and a capacitor line. The light sensing line has a plurality of light sensing cells. The count of capacitors in the capacitor line is smaller than the count of light sensing cells in the light sensing line. The capacitors along the capacitor line store up a portion of the potentials produced by the light sensing cells along the light sensing line.

This invention also provides an alternative CMOS light sensor. The CMOS light sensor has a plurality of light sensing lines and a group of capacitor lines. Each light sensing line has a plurality of light sensing cells and each group of capacitor lines has at least one capacitor line. The count of capacitors in each capacitor line is smaller than the count of light sensing cells in each light sensing line. Furthermore, the potentials produced by the light sensing cells in each light sensing line is transferred in sequence to the capacitor lines in the capacitor line group.

This invention also provides a method of operating a CMOS light sensor. A portion of the light sensing cells in the CMOS light sensor is illuminated to produce a corresponding set of electric charges. Thereafter, the set of unprocessed charges produced by the illuminated light sensing cells is converted into a set of corresponding potentials and transferred to the capacitors on a capacitor line. Finally, the potentials stored in the capacitors of the capacitor line are read out.

In one embodiment of this invention, the CMOS light sensor has a plurality of capacitor lines. When the stored potentials inside one of the capacitor lines is read, a set of unprocessed charges produced by the illuminated light sensing cells is converted into a set of corresponding potentials and transferred to any of the capacitor lines other than the one involved in the reading operation. The potentials in these other capacitor lines are subsequently read according to a pre-defined sequence.

In brief, this invention uses a capacitor line having a count of capacitors smaller than the count of light sensing cells in a light sensing line. Therefore, the time for reading out all the potentials from the capacitors along a capacitor line is shortened. With considerably reduction in reading time, the amount of charges leaking out from each capacitor is minimized and hence the degree of data distortion is reduced considerably.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a conventional CMOS light sensor;

FIG. 2 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a linear CMOS light sensor according to one preferred embodiment of this invention;

FIG. 3 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a staggered CMOS light sensor according to a first preferred embodiment of this invention;

FIG. 4 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a staggered CMOS light sensor according to a second preferred embodiment of this invention;

FIG. 5 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a staggered CMOS light sensor according to a third preferred embodiment of this invention;

FIG. 6 is a timing diagram showing the operating sequence of a CMOS light sensor system having a single capacitor line and at least one light sensing line therein according to one preferred embodiment of this invention;

FIG. 7A is a schematic diagram showing a CMOS light sensor system having a multiple of capacitor lines that correspond to a single light sensing line according to one preferred embodiment of this invention; and

FIG. 7B is a timing diagram showing the operating sequence of the CMOS light sensor system in FIG. 7A.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

FIG. 2 is a schematic diagram showing the relationship between the light sensing lines and the capacitor lines in a linear CMOS light sensor according to one preferred embodiment of this invention. As shown in FIG. 2, the CMOS light sensor 20 includes three light sensing lines 22 a, 24 a, 26 a for sensing the three primary colors red (R), green (G) and blue (B) respectively. In addition, the CMOS light sensor 20 also includes three capacitor lines 22 b, 24 b, 26 b for holding potentials produced by the respective light sensing lines 22 a, 24 a and 26 a. The operational relationship between the three light sensing lines 22 a, 24 a, 26 a and the three corresponding capacitor lines 22 b, 24 b, 26 b are identical. Hence, the operation of only one group of light sensing line and corresponding capacitor line is explained in the following.

In this embodiment, the number of capacitors 221 b˜225 b in the capacitor line 22 b is set to one third of the number of light sensing cells 221 a˜235 a along the light sensing line 22 a. Obviously, the ratio of the number of light sensing cells to the number of capacitors can be varied according to actual application. Since the total number of capacitors 221 b˜225 b in the capacitor line 22 b is only one third that of the number of light sensing cells 221 a˜235 a, data must be extracted in stages from the light sensing cells 221 a˜235 a. The following is a more detailed description of the operation relationship between the light sensing line 22 a and the capacitor line 22 b.

Since the number of capacitors 221 b˜225 b is only one third of the amount of the light sensing cells 221 a˜235 a, the potentials produced by the light sensing cells 221 a˜235 a must be transferred into the capacitor line step by step. Because the potential within the sensing cells 221 a˜235 a are transferred to the capacitor line 22 b in three separate steps, sectional illumination of the CMOS light sensor is preferably. In other words, the light sensing cells 221 a˜225 a are illuminated first followed by the light sensing cells 226 a˜230 a and then the light sensing cells 231 a˜235 a or some other arrangements for these three segments of light sensing cells. Obviously, alternative arrangement such as illuminating the light sensing cells 221 a˜235 a all at once and shifting the resulting potentials into the capacitor line 22 b in sequence is also possible. However, this will increase overall leakage of charges from the sensing cells 221 a˜235 a and lead to a greater data distortion. Whether the CMOS light sensor is illuminated once or in a multiple of exposures, once a set of charges is produced inside the light sensing cells 221 a˜235 a within the light sensing line 22 a, the set of charges are converted into electric potentials and stored inside the capacitor line 22 b. Thereafter, each potential inside the capacitor line is sequentially read to obtain the required image data.

FIGS. 3, 4, 5 are schematic diagrams showing the relationship between the light sensing lines and the capacitor lines in a staggered CMOS light sensor according to this invention. In FIGS. 3 and 4, only one of the three groups (including the capacitor line that corresponds to the light sensing line) of light sensing lines (R, G, B) is shown. Since the remaining two groups of light sensing lines are identical with the one shown in the Figures, their structures are not drawn. In FIG. 3, a light sensing line 32 a is used to capture the intensity of a particular color in the odd pixels of a scan line while another light sensing line 34 a is used to capture the intensity of the same color in the even pixels of the scan line. The capacitor lines 32 b and 34 b are used to hold the potentials after converting the charges that result from the intensity of illumination of the particular color on the light sensing lines 32 a and 34 a. In FIG. 4, both light sensing lines 42 and 44 correspond with one capacitor line 46. In other words, the capacitor line 46 not only stores the resultant potentials captured by the light sensing line 44, but also stores the resultant potentials captured by the light sensing line 42 as well.

In the embodiment of FIG. 5, two capacitor lines 56 and 58 are utilized by light sensing lines 52 r and 54 r used for sensing red color, light sensing lines 52 g and 54 g used for sensing green color and light sensing lines 52 b and 54 b used for sensing blue color. For example, the capacitor line 56 may serve as a storage area for holding the potentials of odd pixels captured by the light sensing lines 52 r, 52 g and 52 b for various colors. Similarly, the capacitor line 58 may serve as a storage area for holding the potentials of even pixels captured by the light sensing lines 54 r, 54 g and 54 b for various colors. If the number of capacitors in the capacitor line 56 is one-third the number of light sensing cells in a single light sensing line (52 r, 52 g or 52 b), all the potentials captured by the light sensing lines 52 r, 52 g and 52 b must be read nine readout operations. Under the same token, all the potentials captured by the light sensing lines 54 r, 54 g and 54 b must be read in nine readout operations. Obviously, this is not the only arrangement for the light sensing lines and the capacitor lines. Persons skilled in the art may change the arrangement to produce optimal results.

After explaining a few light sensing line capacitor line configurations, method of operating the CMOS light sensor is described below. FIG. 6 is a timing diagram showing the operating sequence of a CMOS light sensor system which has a single capacitor line and at least one light sensing line therein. The light sensing line 22 a and the capacitor line 22 b shown in FIG. 2 are used as an example for illustrating the timing diagram in FIG. 6. The clocking signal CK_1 in FIG. 6 is a signal for controlling the light sensing line 22 a and the capacitor line 22 b. When the clocking signal CK_1 is at high potential, potentials captured by the light sensing line 22 a are transferred to the capacitors in the capacitor line 22 b. As the clocking signal CK_1 drops to low potential, the potentials stored inside the capacitors are sequentially read out from the capacitor line 22 b. With this type of timing control, potentials resulted from illuminating the light sensing line 22 a are read out in three separate sessions, namely, session one for reading data 602, session two for reading data 604 and session three for reading data 606. Although this is an arrangement capable of saving a few capacitors in a CMOS light sensor, each data reading session must be punctuated by an idling period t₁. This idling period t₁ is required for transferring the electric potential from the light sensing line 22 a to the capacitor line 22 b. Obviously, the aforementioned arrangement implies that the entire light sensing line 22 a are illuminated all at once and then the generated potentials are transferred in separate sessions. If the light sensing line 22 a is illuminated in several stages, an exposure time period must also be added to the idling time t₁.

To reduce idling time caused by non-successive data transmission, this invention also provides a CMOS light sensor having a plurality of capacitor lines that correspond to a light sensing line. FIG. 7A is a schematic diagram showing a CMOS light sensor system having a multiple of capacitor lines that correspond to a single light sensing line according to one preferred embodiment of this invention. Since the light sensing lines and corresponding capacitor lines for each primary color are the same, only a group that includes a light sensing line 70 and a pair of capacitor lines 73 and 75 is illustrated in detail. The potentials gathered by the light sensing line 70 due to illumination are transferred to the capacitor lines 73 and 75. In this embodiment, the number of capacitors within the capacitor lines 73 and 75 is one-fourth the number of light sensing cells in the light sensing line 70. However, persons skilled in the art may arrange the relative number of capacitors and light sensing cells in any ratio that can optimize overall performance.

FIG. 7B is a timing diagram showing the operating sequence of the CMOS light sensor system in FIG. 7A. In FIG. 7B, a clocking signal CK_2 is used for controlling the capacitor line 73 and a portion of the light sensing line 70 and another clocking signal CK_3 is used for controlling the capacitor line 75 and another portion of the light sensing line 70. For example, when the clocking signal CK_2 is at high potential, the potentials gathered by the light sensing cells 701˜705 or 711˜715 (as shown in FIG. 7A) due to exposure are transferred to the capacitor line 73. When the clocking signal CK_2 drops back to low potential, the potential values are sequentially read from the capacitor line 73 via the end-stage circuit 74. Similarly, when the clocking signal CK_3 is at high potential, the potentials gathered by the light sensing cells 706˜710 or 716˜720 (as shown in FIG. 7A) due to exposure are transferred to the capacitor line 75. When the clocking signal CK_3 drops back to low potential, the potential values are sequentially read from the capacitor line 75 via the end-stage circuit 74. With this arrangement, as long as a proper data length is selected, the data 760, 772, 762, 774 and 764 are linked together to form a continuous data stream. Ultimately, the type of interruption caused by transferring data using a single capacitor line can be avoided.

In summary, this invention provides a means to reduce the time for reading out data stored inside the capacitor line. Hence, the effect charge leakage from the capacitors is greatly minimized. In addition, this invention also provides a structure that uses a plurality of capacitor lines which correspond with a light sensing line and a method of operating this structure. Consequently, very little time is wasted between data transmission and overall operating efficiency of the CMOS light sensor is improved.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1-12. (canceled)
 13. An apparatus, comprising: means for illuminating a portion of light sensing cells within a CMOS light sensor able to produce corresponding electric charges; means for converting a portion of unprocessed charges produced by illuminated light sensor cells to corresponding electric potentials, wherein a number of the unprocessed charges is less than a number of the light sensing cells; means for transferring the electric potentials to a first capacitor line; and means for reading out the electric potentials from the first capacitor line.
 14. An apparatus as claimed in claim 13, further comprising: the CMOS light sensor comprising a plurality of capacitor lines; said converting means being capable of converting the unprocessed charges produced by the exposed light sensing cells into corresponding electric potentials; said transferring means being capable of transferring the electric potentials to one of the capacitor lines other than the a capacitor line while said reading means is reading out the electric potentials of the first capacitor line; and said reading out means being capable of reading out the electric potentials stored within the capacitor lines other than the first capacitor line while said transferring means is transferring the electric potentials of the first capacitor line.
 15. A CMOS light sensor as claimed in claim 1, wherein the potentials captured by the light sensing cells in the second light sensing line due to illumination are able to be transferred to the second capacitor line in segments for storage step by step.
 16. A light sensor, comprising: a light sensing line comprising a count of light sensing cells; and a capacitor line, said capacitor line comprising a count of capacitors smaller than the count of light sensing cells in the light sensing line.
 17. A light sensor as claimed in claim 16, wherein data produced by the light sensing line is capable of being read out in a number of reading operations that is less than the count of light sensing cells in the light sensing line.
 18. A light sensor as claimed in claim 16, wherein a data retaining period of data within the capacitors is less than compared with an arrangement having a greater number of capacitors.
 19. A light sensor as claimed in claim 16, wherein capacitors of the capacitor line are capable of storing up at least a portion of potentials produced by the light sensing cells along the light sensing line.
 20. A light sensor, comprising: one or more light sensing lines, the light sensing lines comprising one or more light sensing cells; and one or more capacitor lines, the capacitor lines comprising a count of capacitors in one or more of the capacitors lines wherein the count is smaller than a number of light sensing cells in one or more of the light sensing lines; wherein potentials produced by the light sensing cells in one or more of the light sensing line are transferred in sequence, or nearly in sequence, to the one or more capacitor lines.
 21. A light sensor as claimed in claim 20, wherein a portion of the light sensing cells is capable of being illuminated to produce one or more electric charges, and wherein unprocessed charges produced by illuminated light sensing cells is capable of being converted into one or more potentials and capable of being transferred to the capacitors on a capacitor line, and potentials stored in the capacitors of the capacitor line are capable of being read out.
 22. A light sensor as claimed in claim 20, wherein if a stored potential inside one or more of the capacitor lines is read, one or more unprocessed charges produced by illuminated light sensing cells is capable of being converted into one or more potentials and capable of being transferred to capacitor lines other than a capacitor line involved in a current reading operation, and potentials in the other capacitor lines are capable of being read according to a pre-defined sequence. 